A simple and general method for preparing polyfluorophenyldiazonium fluoroborates has been developed. The diazonium fluoroborates are the key to successful syntheses of some 3, 3-bis-(2-chloroethyl)-1- polyfluorophenyltriazenes. The electron-withdrawing effect of the polyfluoro groups substantially retards the rate of the cyclization of bis-2-chloroethyl) triazeno group. During development of the coupling of diazonium salts with secondary amines, three 3,3-dimethyl-1- polyfluorophenyltriazenes and two 3,3 bis-(2hydroxyethyl)-1- polyfluorophenyltriazenes have been synthesized and submitted for antileukemic tests. However, in the preparation of 3, 3-bis- (2- chloroethyl)-1-(2, 6-dimethylphenyl) triazene, only the cyclized product can be detected and isolated. Thus, the steric hindrance of 2, 6- dimethyl groups is not effective even for retarding the cyclization. The work on synthesis of the diazirine derivatives as pyrimidine antimetabolites is in progress.